1. Field of the Invention
The present invention relates to vehicle steering control and particularly, but not exclusively, to a steering control apparatus for a vehicle employing a steer-by-wire system in which a steering portion and a steered portion are, during normal use, mechanically disconnected but can be connected mechanically by means of a backup mechanism, such as a clutch, in the event of malfunction. Aspects of the invention also relate to a system, to a controller, to a method and to a vehicle.
2. Background Information
It is known, for example from Japanese Kokai Patent Application No. 2002-145098, to provide a steering control system for a vehicle which is configured to control a steering reaction actuator for the purpose of providing road surface information pertaining to contact between a road surface and the vehicle tires to the driver via the vehicle steering wheel. In this known system, primary and secondary actuators are serially connected to a steering rack and arranged to steer the vehicle wheels by applying a wheel turning torque or force to the steering rack. The actuators are mechanically linked to a backup mechanism in order to provide reliable steering in the event of an accident or a failure of one of the motors. A steering reaction torque for performing steering reaction control is calculated based on a steering angle of the steering rack as measured by a sensor and is used to control the steering reaction actuator thereby to provide steering feedback to the driver.